This invention relates to a suspension assembly having a compound parallelogram arrangement to stabilize an axle seat and an axle hinged together. The invention incorporates a central hanger between tandem axles, two air springs forward and rearward of each axle, and a central upper torque rod that is part of the parallelogram system for both sides of the vehicle, each side having its own parallelogram to stabilize the axle seat.
Various suspension systems heretofore developed have incorporated a parallelogram arrangement or have incorporated a centrally mounted upper torque rod. Some of these suspension systems have incorporated two air springs forward and rearward of an axle. For example, U.S. Pat. No. 4,114,923 issued to John E. Raidel is an example of such a suspension system. U.S. Pat. No. 4,132,432, also issued to John E. Raidel, shows different forms of parallelogram arrangements. U.S. Pat. No. 4,181,323 issued to Raidel shows a central hanger arrangement between tandem axles with two air springs forward and rearward of each axle and with a parallelogram arrangement. None of these suspension systems has the axle seat hinged to an axle bracket with stabilization and control provided by the compound parallelogram arrangement of the present invention.